The present invention relates to a resistor device for controlling a rotational speed of a motor, and more particularly, to a resistor device for controlling a rotational speed of a motor which improves the attaching position of a resistance unit of the resistor device.
Typically, the rotational speed of a motor driving a cooling fan may be gradually controlled by a resistor device. In response to the control of the motor, however, heat is generated from a resistor circuit of the resistor device thereby decreasing the speed control function of the motor and potentially damaging the resistor device when the heat generated is severe.
Accordingly, the resistor device may be cooled by mounting the resistor circuit upon a wide heat sink means of rectangular form and positioning the resistor device in front of an outlet exhausting cooling air produced by the fan. However, it is necessary to position the resistor device in front of the outlet such that the heat sink does not disturb the flow of cooling air from the outlet to other neighboring parts. To avoid restricting the flow of cooling air from the outlet, there are a limited number of ways to position the resistor device.
A conventional resistor device also contains a short circuit means for preventing burning damage to the motor by cutting off the current applied to the motor side when an overload due to a mechanical defect of the motor occurs. Accordingly, a problem exists in preventing the short circuit means from executing as a result of thermal radiation from the resistor circuit. And, there is a further problem that a by-product, such as residual produced upon fusing of the short circuit means, becomes adhered to the resistor circuit.